[CentOS] Why swap if there's still physical memory available

Les Mikesell lesmikesell at gmail.com
Mon Nov 16 23:02:01 UTC 2009


nate wrote:
> yanagik317 wrote:
> 
>> I guess the answer may not be that simple and I most likely haven't
>> described everything that could have influenced the kernel's
>> decision-making, but how does Linux decide how much of a process to be
>> swapped out?  I guess I could read the documentations on the Linux
>> kernel, but does anyone have more general answers ready to be dispensed?
> 
> Linux by default will try to swap less accessed regions of memory
> when memory pressure starts to get tight(say less than 25% of memory
> is free), if you want to override this behavior look to the
> 'swappiness' setting
> 
>> I haven't done anything with sysctl, if that comes into play at all.
> 
> It can if you want
> 
> vm.swappiness = 0
> 
> To tell the kernel not to swap unless it *really* needs to
> 

Also, the top values may not tell the whole story - RES should include 
paged-in code plus memory allocated by the program.   VIRT includes code 
not paged in yet and linked shared libraries, so the difference may not 
all be in swap.

-- 
   Les Mikesell
    lesmikesell at gmail.com


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